1. Field of the Invention
The present invention relates to a variable valve which functions as an intake valve or an exhaust valve of an internal combustion engine mounted on a vehicle or the like. More specifically, the present invention relates to a control apparatus for and a control method of controlling an electromagnetically driven valve to perform fail-safe processing if abnormality occurs in the electromagnetically driven valve.
2. Description of the Related Art
Conventionally, the electromagnetically driven valve is provided with: a valve body which functions as the intake valve or the exhaust valve of the internal combustion engine; and a movable needle which is connected to the valve body and which displaces in the axial direction of the valve body. Hereinafter, the valve body and the movable needle are referred to as a “movable portion”, as occasion demands. The exhaust valve or the intake valve can be opened and closed any time (i) by supplying an exciting current to an electromagnetic coil for valve-closing or an electromagnetic coil for valve-opening at an appropriate timing, thereby to generate an electromagnetic power, in order to suction the movable needle which is held at a middle position by the elastic force or applied force of a spring, and (ii) by displacing the movable portion to the side of the electromagnetic coil for valve-closing or the side of the electromagnetic coil for valve-opening.
For example, Japanese Patent Application Laying Open NO. 2002-81329 discloses a technique of controlling the electromagnetically driven valve to supply a proper exciting current to the electromagnetic coil for valve-closing and the electromagnetic coil for valve-opening, in order to properly and surely move or displace the valve body between a fully closed position (i.e., a condition of “seating for valve-closing”) and a fully opened position (i.e., a condition of “seating for valve-opening”) of the electromagnetically driven valve. However, it can be assumed that an operation of valve-opening or an operation of valve-closing does not succeed completely or perfectly, (i) from a cause by a change with the passage of time, such as a change in mass of the movable portion and a change in a friction force by the wear of the spring, by the accumulation of deposits onto the movable portion, by abrasion, or the like, and (ii) from an unexpected or sudden cause, such as a reading error of a lift sensor and a foreign body stuck between the valve body and a valve seat.
For example, Japanese Patent Application Laying Open NO. Hei 11-132017 discloses a technique of preventing the step-out of the valve body by increasing an electromagnetic force which suctions the movable portion in the displacement direction by supplying the exciting current to the electromagnetic coil if a deviation between a detected displacement amount of the electromagnetically driven valve and a desired displacement amount is greater than or equal to a threshold value. Here, the “step-out” is such a phenomenon that the valve body of the electromagnetically driven valve is held at a neutral position while the valve opening or closing of the electromagnetically driven valve is driven and that the valve opening or closing cannot be normally driven.
For example, Japanese Patent Application Laying Open NO. 2001-159331 discloses a fail-safe technique of controlling the electromagnetically driven valve to maintain it in the fully closed position by increasing an exciting current amount of the electromagnetic coil for valve-closing, thereby to close the valve, if the electromagnetically driven valve is opened and fails in seating for valve-opening. There is another technique disclosed in Japanese Patent Application Laying Open NO. Hei 11-294209.
However, it is impossible to attain such fail-safe processing that a pressure condition and a combustion condition or the like in a cylinder obtained after the electromagnetically driven valve is maintained in the fully closed position are considered, only by controlling the electromagnetically driven valve by the conventional fail-safe technique for the electromagnetically driven valve, which is disclosed in the above-described Japanese Patent Application Laying Open NO. 2001-159331 or the like, so as to maintain it again in the fully closed position if the electromagnetically driven valve fails in the seating for valve-opening. This possibly causes the reduction of exhaust efficiency, the reduction of filling efficiency for an intake air, the step-out of the electromagnetically driven valve, or the like, and eventually causes a decrease in the output of the internal combustion engine, the deterioration of exhaust emissions, or the like, which is a technical problem.